Lessons from the Great Hanshin EarthquakeReport for the XIX UIA Barcelona Congress,
July 1996Takekuni Ikeda, Ph.D

Good afternoon, ladies and gentlemen. Today Id like to talk to you about the Great Hanshin Earthquake, what weve learned from it, and how all this relates to my urban-planning philosophy.

This quake hit the Hanshin-Awaji areahence its official name, the South Hyogo-Awaji Earthquake of 1995early on January 17th last year, causing devastation along active faults associated with the Rokko Mountains and Awaji Island. Most of the damage was concentrated in a corridor about thirty kilometers long and one to two kilometers wide. Unfortunately, this is a densely populated area, and over 6,300 lives were lost. Material damage is estimated to have topped 100 billion dollars.

For Japan, a country used to earthquakes, this 7.2-magnitude quake was not remarkably bigthe 1891 Nobi Earthquake was magnitude 8.4, and the Great Kanto Earthquake of 1923 registered 7.9. But this direct-hit on a conurbation dealt a lethal blow to virtually the entire infrastructure: from railways to harbors; all the lifelines; and structures ranging from simple wooden houses to modern skyscrapers.

At the time of the earthquake, Kobe was the sixth largest city in Japan with a population of over 1.5 million. It was considered a model cosmopolitan city. Reflecting on the enormous damage done by nature to this modern city, I feel tremendous responsibility as an architect, for our structures turned out to be much more fragile than anyone imagined.

Kobe has escaped the large earthquakes of modern times; indeed, the city hasnt experienced a major seismic event for several hundred years. This is one reason for city officials, citizens, and architects alike being more concerned about the annual threat of typhoon damage than the potential for earthquake damage. Theres no denying that the city was inadequately prepared for this contingency. The deeper our investigations probe, the more we realize how numerous and wide-ranging are the lessons we must learn. To me, its clear that many of the factors that exacerbated this disaster stem from the egocentricity of modern human civilizationthe way we unconditionally subjugate nature.

Look at our exploitation of the forests in the Rokko Mountains; theyve been felled and the soil used to reclaim land from the sea. Here is a modern city taking complete control of nature on the whim of us humans. Its no exaggeration to say that this kind of modernization completely ignores the importance of the flora and fauna that finds its niche in our mountains and seas.

Over geological time, landslides and sedimentation have been driven by natural forces, maintaining a natural balance in the environment. But our rapid, artificial changes to natures subtle balance risk not only the destruction of an ecosystem that has slowly evolved over the millennia, but also the creation of extremely fragile systems that are increasingly vulnerable to disaster. We have to consider this aspect in our engineering schemes.

The ground failures, subsidence of reclaimed land, liquefaction, and loss of lifelines and city infrastructure that resulted from this latest quake are, in large part, attributable to nonchalance about the way we have altered nature. Let me examine some specific examples.

The layout of modern Kobe and earthquake damage

Central to Kobes topography is a river system that flows down from the Rokko mountain range-mountains that, along with the sea, defined the shape of Kobe until the beginning of this century. It could be said that, until then, peoples lives were informed by harmony with nature.

Most structures destroyed by the Great Hanshin Earthquake were concentrated in areas developed since the turn of the century. The worst devastation occurred on what was a marshy deltaup to around 2,000 years ago it was part of the sea. The marsh gradually filled with sediment brought down by rivers from the Rokko Mountains, and long ago it was turned into paddy fields.

Research by environmental archeologist Manabu Takahashi shows that little damage was done on an ancient sand bank that surrounds this areaeven to tile-roofed wooden houses, which generally suffered most from this earthquake. Most of the devastation occurred within the sand bank, in an area which was once a lagoon.

Topographical maps from 1887 show that local people lived on the sand bank, while the former lagoon was still being farmed. After the turn of the 20th century, though, city expansion forced much of the area into use as residential land; by about 1920 it was fully developed.

In the 1960s, the Japanese economy expanded rapidly after recovering from the damage of World War II. Kobe was the first large city to carry out major city-center redevelopment. The demand for residential land skyrocketed, and Kobe began expanding inland and outward into the sea. Soil was taken from the mountains to reclaim land, and public-service facilities and apartment complexes were built on the leveled mountain tracts. Rokko Island and Port Island were built, as were the harbor facilities that characterize modern Kobe.

This process largely ignored the natural environment in a quest for efficiency: a modus operandi typical of Japans urban-development practices since the war.

Damage resulting from mountain and seashore development

What were the implications for all this in the Hanshin earthquake? On the lower slopes of the Rokko Mountains, where hill tops had been leveled for development, the ground failed at some 2,000 locations; many died when homes and buildings were buried by landslides.

Harbor facilities that had been built on landfill were damaged. Quaywalls shifted seaward as the ground under them subsided, and ground failures, subsidence, and displacements were observed on the landward extremities of reclaimed areas. One sinkhole was three and a half meters deep! Freight-handling equipment collapsed and many breakwaters sank. About one-third of Japans international ocean freight and one-tenth of its ferry capacity were paralyzed, with serious negative effects on the Japanese economy.

Wherever land had been reclaimed over the past thirty years or more, muddy water gushed out when liquefaction occurred. Ground subsidence was widespread, causing severe damage to underground lifeline facilities. While there was little visible damage to tall buildings aboveground, damage to their foundations was considerable. Weve seen this before, in the 1964 Niigata Earthquake: then, too, buildings with little above-ground damage continued to be used. But twenty years on, when the foundations were uncovered during redevelopment, the destruction of foundation pilings was seen for the first time.

Damage to lifelines

The Kobe quake left over 860,000 homes without gas, over 960,000 without water, and some 100,000 telephone lines out. A million homes had no power. Electricity was completely restored in a week, and telephones were up in about two; but it took over two months to fully restore drinking water and gas.

Kobes lifelines operated on a large, integrated hierarchy, unlike the decentralized networks that Tokyo and other areas have turned to. The weaknesses of such integrated systems were made painfully apparent. Also, a shortage of local fire-water tanks meant that there was inadequate water for fighting fireshence the huge number of residential and industrial buildings that burned to the ground, even though the day of the quake was windless. Water from nearby rivers could not be used, either: the shallow watercourses had been reinforced on three sides by concrete levees, so the water wasnt deep enough to allow pumping.

A citys rivers are crucial to preserving its environment. In Kobe, these valuable rivers have been lined with concrete for the sake of more efficient land use. Not only has this destroyed their amenity value and contributed to environmental problems, but it has also made them useless for fire-fighting.

Rokko Island and Port Island are similar examples of damaged local ecosystems. These gigantic reclamation projects were carried out in the name of bolstering the economy. Although the modern hospitals and high-rise residential complexes on the islands suffered little damage, they were functionally paralyzed as a result of damage to lifelines. Hospital patients and residents had to be relocated until restoration was possible.

Damage to the city infrastructure

Lets look at the damage incurred by the citys infrastructure. The major urban transport systemsrailways, highways, and subwayssuffered severe destruction everywhere. This was a serious impediment to all emergency operations, and routine economic activities were also thrown out of kilter.

The roots of this enormous damage are to be found in changes made to the natural environment. For example, the elevated tracks for Japans most advanced railway, the Bullet Train, collapsed at eight locations. At a cursory glance, the ground in these locations is indistinguishable from any other; but geological archeologists point out that it corresponds to old riverbeds where, sometime in the past 3,000 years, water once flowed.

One section of elevated highway, hundreds of meters long, rolled over on its side; others, apparently identical, suffered little or no damage. This type of localized damage could be seen everywhere.

Detailed investigations and aerial photographs reveal what was not clear at ground level: piers that keeled over were on the land that was submerged 2,000 years ago, whereas adjacent piers left standing were on the old sand bank. Theres a now-famous photo of a bus, its front half hanging precariously over the edge where the highway collapsed. While traveling down the Hanshin Expressway, the driver suddenly saw the road in front of him begin to pitch and roll. He slammed on the brakes and managed to stop just in time. Interestingly enough, the collapse was right on the boundary between what had been the lagoon and the sand bank.

So we see that many of the piers and bridge beams that collapsed, and many of the locations where the ground shifted, were on land that had been backfilled or reclaimed recently. Even the subwayswhich are supposed to hold up well in earthquakessuffered from collapse and ground subsidence where they passed through the old lagoon.

Damage to earthquake-resistant structures

Since the 7.9-magnitude Great Kanto Earthquake of 1923, which claimed over 140,000 lives, engineers have been making step-by-step improvements to earthquake-resistant design techniques. Buildings that conform to the latest 1981 revision of the Earthquake-Resistant Design Law, which specifies dynamic seismic response analysis, largely escaped serious damage. Yet a new eight-story wing of Kobe City Hall was among many buildings laid waste along Sannomiyas main street. All of these damaged buildings stood on land that was part of the Ikuta River a hundred and twenty years ago. To make way for the modern city, the natural Ikuta River was diverted into a new channel, and the old one was backfilled.

Lessons from the Great Hanshin Earthquake and tasks for the future

Harmony with nature

To me, it goes without saying that when we tamper with nature without adequate thoughtby cutting into mountains, changing the course of rivers, and filling in the seawe damage the natural environment which we humans have to share with all living creatures. Nature has now given us a pretty strong warning: these changes result in an extremely fragile urban structure; one that invites greater disaster in the face of earthquakes, typhoons, and other natural calamities. We must learn this valuable lesson and use it in our future plans for city construction, carefully considering whether our actions will maintain harmony with nature or not.

Diagnosis of existing structures for earthquake resistance and retrofitting

The fact is that most Japanese cities have already made such damaging changes to nature. Recognizing that our cities do have this inherent vulnerability, I think we need to examine the measures we can take to avert future disaster. Structures built before the new 1981 design lawmany of the heavily damaged structures in Kobeneed to be diagnosed to check their earthquake-resistant performance. They must be retrofitted as required. New legislation enacted in autumn 1995 facilitates the retrofitting of existing structures throughout Japan, and a number of subsidies are being expanded to this end. We are also training architectural engineers to carry out the needed structural diagnosis.

Further, in October 1995, the Japan Institute of Architects drew up new guidelines and held seminars for architects and their clients on earthquake-resistance retrofitting. By constructively passing on the lessons learned from the Great Hanshin Earthquake, they are taking some of the responsibility for preventing future disasters.

A system for setting minimum levels of earthquake-resistance according to a buildings importance to the community

Conventional earthquake-resistant design is based on the idea that buildingsaside from nuclear power plants and other special structures that have to withstand anythingshould protect peoples lives even if, in a worst-case scenario, they are damaged beyond repair or destroyed. However, it is now clear that we must provide certain critical buildings with better protection; hospitals, police stations, and firehouses, for example, must retain their functionality in times of disaster.

One thing the Great Hanshin Earthquake taught us is that we need to develop a system for assessing and setting minimum levels of aseismic performance according to a buildings importance to the community. Each building would be assigned a level of importancean importance coefficient, shall we call it?depending on its public function. Recognition of this need, prompted by the Kobe quake, has led to studies on ways to ensure that function is maintained. These include such quake-resistant systems as base-isolation or damping, and improvements to levels of emergency-supply storage according to the value of this coefficient.

The still unknown power of earthquakes

Every earthquake teaches us a great deal, and this one was no exception. Seen another way, this means that despite all the great advances we have made, there is still much we do not understand about earthquakes. This time, for example, we saw the destruction of large elevated steel-frame structures which turned out to be more fragile than we supposed. We saw the collapse of mid-level floors of supposedly earthquake-resistant buildings. And there were numerous other examples of unusual displacement, and of vertical forces that far surpassed anything we had imagined.

Much of the evidence strongly suggests the existence of seismic shockwaves. But because we are still unable to measure them, the mechanism of vertical shockwave transmission within 10 kilometers of the epicenter is still unknown. It has also proved impossible to verify them through experiments. As a result, no opinions have yet been offered publicly on the matter.

And there is still much we dont understand about the transmission of seismic forces into buildings, though this is a fundamental question we have to consider in formulating preventive measures. All of this indicates just how urgent further research is. We need greater exchanges of data between countries, as well as more cooperative research efforts.

Publication of a textbook on earthquake-resistant design

Weve learned a great deal from the Great Hanshin Earthquake, much more than Ive touched on. In such a limited time, itd be impossible to mention everything. But, as architects, we must be aware of all of them. To help with this, the Japan Institute of Architects is compiling a new textbook for experienced architects on earthquake-resistant design. We hope it will be useful as they work in earthquake-prone Japan. Its nearly finished, and will soon be ready for publication.

In conclusion

I wonder: have we not put too much trust in modern technology, and taken too arrogant an attitude toward nature? I cannot help but feel that the Great Hanshin Earthquake poses a difficult question for us humans as we mold nature to our convenience. Weve put ourselves at the center of everything, but are we not ignoring the bountiful earth that makes it all possible?

Perhaps we need to free ourselves from the idea of mankind at the center of everythingfaith in the omnipotence of science and technology. I think we must examine once again the relationship we share with other living things; with all of nature. Perhaps what we find will teach us how we should plan our cities.

Thank you.

Translated and edited by Linda Yabushita, James Lockhart, and Stephen Cassidy. Originally posted: 17 October 1996. Updated: 14 November 1999. Reformatted: 15 March 2010.